Recently, in terms of recovery of carbon dioxide, a carbon dioxide recovery and storage technique attracts attention as an effective measure against a globally-concerning global warming problem. Especially, for exhaust gas from a thermal power plant and the like, a method for recovering carbon dioxide by an alkaline aqueous solution is considered.
As such a carbon dioxide recovering apparatus is known one including an absorbing tower causing carbon dioxide contained in the flue gas to be absorbed in an absorbing solution to generate a rich solution, a releasing tower heating the rich solution discharged from the absorbing tower to release and separate carbon dioxide as well as steam and returning a generated lean solution to the absorbing tower, a first heat exchanger allowing the lean solution supplied from the releasing tower to the absorbing tower to pass therethrough, a second heat exchanger allowing carbon dioxide containing steam separated in the releasing tower to pass therethrough, and a flow distributor dividing and supplying the rich solution discharged from the absorbing tower to the first heat exchanger and the second heat exchanger and adapted to cause the rich solution introduced into the first heat exchanger and the second heat exchanger to heat-exchange with the lean solution and the carbon dioxide containing steam, respectively, and to thereafter be supplied to the releasing tower.
In the aforementioned conventional carbon dioxide recovering apparatus, in a case where a divided flow rate to the second heat exchanger is lower than an optimum value, heat exchange with the carbon dioxide containing steam is not performed sufficiently. On the other hand, in a case where the divided flow rate to the second heat exchanger is higher than the optimum value, heat exchange with the carbon dioxide containing steam is performed sufficiently, but a temperature of the rich solution heated in the releasing tower is lowered, and a releasing performance of carbon dioxide is degraded. This case causes a problem in which the lean solution from which carbon dioxide is not released sufficiently is sent to the absorbing tower, and in which carbon dioxide in the exhaust gas cannot be absorbed sufficiently in the absorbing tower. An increase in energy to be provided to a reboiler to avoid this situation results in an increase in energy required for recovery of carbon dioxide.